Computer systems employ a wide variety of peripheral components or input/output (I/O) devices. For example, a typical computer system usually contains a monitor, a keyboard, a mouse, a network controller, a disk drive or an array of disk drives, and, optionally, a printer. High performance computer systems such as servers have more complex I/O device requirements.
An example of a host processor of a computer system connected to I/O devices through a component bus is defined by the PCI (peripheral component interconnect) Local Bus Specification, published by the PCI Special Interest Group. During system initialization, the host processor loads a device driver for each PCI device on the PCI bus. A typical PCI device includes multiple configuration registers located within a configuration memory space of each respective PCI device. The configuration registers including identification registers, such as, for example, the vendor ID, device ID or revision register, are read by the device driver and the host system during the initialization or normal operations to identify the PCI device. Typically, the identification registers are hardwired to fixed values during the manufacturing processes of the PCI device and they are not modifiable by the device driver or the operating system (OS) of the host. As a result, a legacy device driver that is looking for specific identification of a PCI device will not work with a PCI device having different identification information, such as, a different vendor ID or a different device ID, etc.
PCI Express (PCIe) is an improvement over PCI and defines a high performance, general purpose I/O interconnect for a wide variety of computing and communications platforms. Key PCIe attributes, such as the PCI usage model, load-store architectures, and software interfaces, are maintained in PCIe, but PCI's parallel bus implementation is replaced in PCIe with a highly scalable, fully serial interface. PCIe takes advantage of advanced point-to-point interconnects, switch-based technology, and packetized protocols to deliver improved performance features.
Input/Output Virtualization (IOV) is a name given to the capability of an I/O device to be used by more than one operating system (OS—sometimes called a system image) running on the same or different CPUs. Modern computing and storage systems use IOV because IOV offers improved management of information technology resources through load balancing and effective use of underutilized resources. For example, IOV allows a limited set of resources, such as computer memory, to be more fully used, with less idle time, by making that resource available on a shared basis among a number of different operating systems. Thus, instead of having separate memory for each OS, where each separate memory is underused, a shared memory is available to all operating systems and the shared memory experiences a higher utilization rate than that of any of the separate resources.
While computing and communications systems incorporating PCIe technology are proliferating, many legacy (e.g., PCI) systems remain in use. When such legacy systems are mated to the newer PCIe systems, communications between these legacy systems and the newer PCIe systems can create problems.